feature: acceptance tests

[roxblnfk]

Reason for This PR

Adds acceptance tests to verify the integration between RoadRunner Temporal plugin, PHP SDK, and Temporal.

Description of Changes

• Added acceptance tests infrastructure in tests/acceptance/
  • Included PHP SDK as a git submodule for testing
  • Created README with setup instructions for running tests
• Added Github Workflow

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [ ] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.